Project 2: Overhauser enhanced Magnetic Resonance Imaging. (OMRI) We have examined several tumor models in mice to evaluate the image enhancement profiles. Different tumor types were grown in mice and OMRI experiments were carried out using Oxo 63 as the contrast agent when tumors were at the size of 1 ml. Enhancement profiles were found to be significantly varied in the tumors examined. The melanoma cell line B16 exhibited the highest enhancement where as the SCC cell line (squamous cell carcinoma) exhibited the least enhancement. Other cell lines such as the RIF-1, HT-29 exhibited intermediate enhancement. Additional experiments with conventional contrast enhanced MRI using Gd3+-DTPA on these animals with different tumors showed time -intensity profiles in images which had different behavior in each tumor type tested. Histologic studies quantitating the microvessel density in tumors are proposed to be carried out to study the dependence of image enhancement vs tumor perfusion.